Method for manufacture of noble metal alloy catalysts and catalysts prepared therewith

ABSTRACT

The present invention provides a method for manufacture of supported noble metal based alloy catalysts with a high degree of alloying and a small crystallite size. The method is based on the use of polyol solvents as reaction medium and comprises of a two-step reduction process in the presence of a support material. In the first step, the first metal (M1 =transition metal; e.g. Co, Cr, Ru) is activated by increasing the reaction temperature to 80 to 160° C. In the second step, the second metal (M2=noble metal; e.g. Pt, Pd, Au and mixtures thereof) is added and the slurry is heated to the boiling point of the polyol solvent in a range of 160 to 300° C. Due to this two-step method, an uniform reduction occurs, resulting in noble metal based catalysts with a high degree of alloying and a small crystallite size of less than 3 nm. Due to the high degree of alloying, the lattice constants are lowered. The catalysts manufactured according to the method are used as electrocatalysts for polymer electrolyte membrane fuel cells (PEMFC), direct-methanol fuel cells (DMFC) or as gas phase catalysts for CO oxidation or exhaust gas purification.

BACKGROUND OF THE INVENTION

The present invention provides a method for manufacture of noble metalalloy catalysts. The method is based on the use of polyol solvents asreaction medium. The catalyst manufactured according to the inventionare characterized by a high degree of alloying and a very smallcrystallite size. They can be used as electrocatalysts for polymerelectrolyte membrane fuel cells (PEMFC), direct-methanol fuel cells(DMFC) or similar electrochemical devices. Furthermore, they aresuitable as catalysts for CO-oxidation reactions (PROX) or exhaust gaspurification.

In principle, fuel cells are gas-operated batteries, in which thechemical energy obtained from the reaction of hydrogen and oxygen isconverted directly into electrical energy. The present inventiondescribes catalysts for PEM fuel cells (PEM=polymer electrolytemembrane), which are suitable for operation with hydrogen-containinggases or with methanol (DMFC=direct methanol fuel cell). Fuel cells aregaining increased importance as mobile, stationary or portable powersources.

Electrocatalysts based on platinum (Pt) are routinely used on the anodeand cathode side of PEM fuel cells. They comprise of finely dividednoble metal particles, which are deposited on a conductive supportmaterial (generally carbon black or graphite). Normally, theconcentration of noble metal is in the range from 10 to 90 wt. %, basedon the total weight of the catalyst.

Conventional platinum anode catalysts are very sensitive to poisoning bycarbon monoxide (CO). Therefore the concentration of carbon monoxide(CO) in the anode gas has to be reduced to the ppm-range in order toprevent performance losses in the fuel cells due to poisoning of theanode catalyst. It is known that the tolerance of a platinum catalyst topoisoning by carbon monoxide (CO) can be improved by alloying theplatinum with ruthenium (Ru). Generally, this means that oxidation ofthe carbon monoxide adsorbed on the platinum to carbon dioxide (CO₂)takes place and the CO₂ is then readily desorbed.

For the cathode side of PEMFCs, frequently pure PVC catalysts are used.As some Pt alloy catalysts, comprising Pt and the base metals Co, Cr orNi offer an activity enhancement by the factors of 1,5 to 3 (ref to U.A.Paulus, A. Wokaun et. al, J. Phys. Chem. B, 2002, 106, 4181-4191), thesealloy compositions are more frequently used for cathode catalysts.

The present invention refers to the manufacture of nano-sized noblemetal catalysts via the colloid route. Various processes for manufactureof noble metal colloids in water-based systems are known:

EP 1 175 948 discloses noble-metal containing nanoparticles, which areembedded in an aqueous solution of a temporary stabilizer. Thenanoparticles are manufactured by reduction of chloride-free precursorcompounds in water in the presence of a polysaccharide. The nanoparticlematerials are used for catalyst inks, catalyzed ionomer membranes andfor the manufacture of electrocatalysts.

U.S. Pat. No. 5,925,463 describes metal, bi-metal and multi-metalcolloids with particle sizes up to 30 nm. The colloids are stabilized bywater-soluble stabilizers.

EP 423 627 B1 is directed towards the preparation of microcrystalline oramorphous metal or alloy colloids obtainable by reduction with metalhydrides in organic solvents.

EP 796 147 B1 and DE 44 43 705 disclose surfactant-stabilized colloidsof mono- and bimetals of the groups VIII and IB of the Periodic Systemof the Elements (PSE) having particle sizes in the range of 1 to 10 nm.They are prepared by reduction in water in the presence of stronglyhydrophilic surfactants.

EP 924 784 B1 teaches alloyed PtRu/C catalysts with a medium particlesize in the range of 0.5 to 2 nm. These alloy catalysts were prepared byfixing a PtRu colloid (obtained according to EP 423 627 B1) on a carbonblack support at temperatures up to 50° C. The degree of alloying isrelatively low, a lattice constant of 0.388 nm is reported.

More specifically, the present invention refers to a catalystmanufacturing process in polyol solvents as reaction medium (the “polyolprocess”). Similar processes have been recently published in the patentliterature.

JP 11 246 901 provides a method for producing stable metal particlesdeposited on a porous carrier by dissolving a metal salt in a polyhydricalcohol (“polyol”). A pH-adjusting agent is added to adjust the pH valueto prevent agglomeration of the particles.

U.S. Pat. No. 6,551,960 discloses the preparation of supported,nanosized catalyst particles, particularly PtRu particles, via a polyolprocess. A solution of platinum and ruthenium compounds in apolyhydroxylic alcohol solvent is mixed with an electrically conductivesupport material and subsequently heated to a temperature in the rangeof 20 to 300° C. to reduce the Pt and Ru to a zero valence state and toform PtRu catalyst particles with less than 1 micron particle size. Thepresent inventors have reproduced this method. It was found that, due tothe different reaction rates for the two elements in the processemployed, the PtRu alloy formation is not complete (i.e. a low degree ofalloying is obtained).

US 2003/0104936 A1 describes nanoparticle catalysts and a method ofmaking them in a polyol process. A solution of metal chlorides of one ormore catalyst metals in a polyalcohol solvent is converted to acolloidal particle suspension by raising the pH and heating thesolution. This colloidal suspension is then combined with the supportmaterial and the nanoparticles are deposited by lowering the pH of thesuspension. A mixture of metal compounds is used and the metal compoundsare simultaneously reduced.

U.S. Pat. No. 5,856,260 refers to the preparation of high activitycatalysts. A solution of polyol is employed to impregnate and disperse acompound of a catalytic metal on an inorganic oxide support. Noble metalcontaining alloys are not disclosed.

SUMMARY OF THE INVENTION

It was an objective of the present invention to provide an improvedmethod for manufacturing of noble metal based alloy catalysts in polyolsolvents as reaction medium (“polyol process”). The catalysts preparedaccording to this method are supported on a carrier material, show ahigh degree of alloying and a small crystallite size of less than 3 nm.

It was a further objective of the invention, to provide a manufacturingprocess for noble metal based alloy catalysts, which avoids expensiveand time-consuming heat treatment and/or calcination processes for alloygeneration.

It was still a further objective of the invention, to provide amanufacturing process for noble metal based alloy catalysts, whichavoids particle agglomeration, sintering and particle growth, commonlyassociated with heat treatment and/or calcination processes.

It was another objective of the invention, to provide Pt alloycatalysts, particularly PtRu and PtCo catalysts, with a high degree ofalloying and a small crystallite size of less than 3 nm (as determinedby XRD analysis).

These objectives were met by the method disclosed in the presentinvention. The method is based on a two-step, sequential reductionprocess. In the first step, the precursor compound of the first metal(M1; a base metal or a “less noble” metal such as ruthenium) isactivated by adjusting the reaction temperature in a range of 80 to 160°C. In the second step, the precursor compound of a second and/or thirdmetal (M2; the noble metal(s) such as platinum, palladium, gold ormixtures thereof) is added to the slurry. After a certain period oftime, the temperature is further increased in a range of 160 to 300° C.Due to this two-step method a uniform reduction process occurs, leadingto noble metal based particles with a high degree of alloying and asmall crystallite size. In the presence of a suitable support material,the alloy particles are deposited on the support surface.

DETAILED DESCRIPTION OF THE INVENTION

Surprisingly, it has been found that the degree of alloying issubstantially improved by the two-step method disclosed in the presentinvention. The first metal MI (e.g. a base metal) is activated prior tothe addition of the second metal (M2, a noble metal, preferablyplatinum). This activation is achieved by heating the polyol solutioncontaining the first metal (M1) to a temperature in the range of 80 to160° C.

As an example, the effect is explained in the Pt-Ru system. The thermalenergy added to the system increases the reduction rate (V₁) for thereduction of the first metal (M1, in this case the Ru³⁺compound). At thepoint when the second metal (M2, the Pt compound) is added, thereduction rate (V₂) for the Pt compound and the reduction rate for theRu compound (V₁) become nearly identical:

Condition for a high degree of alloying: V₁˜V₂

The same correlations apply to the two-step reduction process of basemetals (M1=Co, Ni, Cu etc) in the presence of noble metals (M2=Pt, Pd orAu etc). As a result of the two-step method, catalysts comprising ofparticles with a high degree of alloying are obtained.

It should be noted, that for the second step the noble metal (M2) cancomprise of a mixture or a combination of various noble metals, such asfor example Pt+Au, Pt+Pd or Pt+Rh. Thus, ternary Pt-based alloy catalystsystems (e.g. PtCoAu, PtRuAu) can be manufactured. Typically, theternary alloy catalysts comprise between 0.1 to 5 wt. % of a secondnoble metal (other than Pt) based on the total weight of the catalyst.

As the alloying step does not need any heat treatment, sintering effectsare avoided. The alloy particles prepared by the present method are verysmall in size. Typically, the medium crystallite size is less than 3 nm(as detected by XRD analysis)

The X-ray diffraction (“XRD”) analysis is performed on powdered catalystsamples with a powder diffractometer manufactured by STOE Co,Darmstadt/Germany using Cu—Ka radiation. The diffractograms are recordedin reflexion mode in the 2 θ-range of 20 to 120°, the two peaks forface-centered Pt (1,1,1) and Pt (2,0,0) are monitored.

For the Pt-based alloy catalysts of the present invention, alloying isobserved by a shift of the Pt peaks towards higher values of 2 θ. Inaddition to that, peaks associated to a non-alloyed component (forexample free Co or free Ru) are not detected in the XRD spectra.

The degree of alloying is determined by the lattice constant of the Ptalloy particle. The lattice constant again is derived from XRD analysis.According to VEGARD's law, a lattice contraction occurs due to thealloying process. In the case of Pt, this results in a lower value ofthe lattice constant of the Pt-alloy catalyst compared to pure Pt. Ingeneral, the higher the degree of alloying, the lower is the latticeconstant.

The lattice constant for pure Pt is 0.3923 nm (ref to ICDD data base;International Center for Diffraction Data, Campus Boulevard, NewtonSquare, Pa., USA). Due to the high degree of alloying, the noble metalbased catalysts of the present invention have lattice constants, whichare considerably lower than this value.

In the present invention, the term “alloy” means a solid solution of thefirst metal component (M1) in the fcc (face-centered cubic) lattice ofthe second metal component (M2). There are no ordered phases orintermetallic compounds present. Such ordered phases are obtained byemploying high temperatures in the range of 600 to 900° C. in commonheat treatment processes. Therefore, the corresponding signals forsuper-lattices (for example of the AB3-type) not detected in the XRDspectra.

The first metal (M1) is a base metal selected from the group oftransition metals of the Periodic System of Elements (PSE). Examples aretitanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper,zinc, zirconium, niobium, molybdenum, tantalum, tungsten and rhenium.Furthermore, ruthenium, although a member of the group of noble metals,is part of this first group (M1) due to its “less noble”characteristics.

The second metal (M2) is a noble metal selected from the group ofplatinum, silver, palladium, rhodium, gold, iridium and mixtures orcombinations thereof. Preferably, platinum and a combination of platinumand gold (PtAu) or platinum and palladium (PtPd) is used.

In a typical manufacturing process, the carbon support material (e.g.XC72R, Cabot Inc.) is suspended in the polyol, e.g. DEG (diethyleneglycol) or PG (propylene glycol). Optionally, the polyol solvent maycontain a protective colloid or stabilizer, such as arabic gum. Then theprecursor compound of the first metal (M1) is added. The mixture issubsequently heated to 80 to 160° C. with constant stirring. In thisstage, the precursor compound of M1 is activated. In the case of Ru, theprecursor compound is partly reduced from Ru³⁺ to Ru²⁺ and a change incolor is sometimes visible.

After having reached a certain temperature in the range of 80 to 160°C., the precursor compound of the second metal (M2, preferably Pt or amixture of Pt with another noble metal) is added. When the addition iscompleted, the suspension is finally heated to the boiling point of thepolyol solvent (T_(bp)) and maintained there for a minimum of 30 mins.

Optionally, the process may contain an additional step to destroy theprotective colloid. After the final heating step, an acid is added whilethe suspension is maintained at temperatures in the range of 100 to 110°C. Alternatively, the protective colloid can be destroyed by addition ofalkalis such as NaOH.

The suspension is cooled down to room temperature and the catalyst isseparated, washed chloride-free and dried. For many fields ofapplication, the catalyst may be used in this condition. For certainspecial applications, it may be advantageous to calcine the catalystafterwards under an inert or reducing atmosphere at temperatures between300 and 1000° C.

Suitable precursors for the first metal (M1) are chlorides, nitrates,carbonates, hydrogencarbonates, basic carbonnates, sulfates, nitrites,acetates etc. of the transition metals. Examples arecobalt(II)-chloride, cobalt(II)-nitrate, cobalt(II)-hydroxide-carbonate,cobalt(II)-carbonate, copper(II)-acetate, chromium(III)-nitrate,manganese(II)-sulfate etc. Suitable precursors for Ru areruthenium(III)-chloride, ruthenium acetate, ruthenium nitrosyl-nitrateand similar compounds;

Suitable precursors for the second metal (M2, noble metal) are forexample bis-ethanolamine-hexahydroxo-platinate [“EA-platinum” or(EA)₂Pt(OH)₆]), hexachloro-platinum acid (“CPA” or H₂PtCl₆), platinumnitrate and other Pt precursor compounds. A suitable precursor for Au isfor example gold(III)-chloride (AuCl₃), for Pd preferablypalladium(II)-nitrate or palladium chloride is used.

Examples for suitable polyol solvents are 1,2-ethylene glycol (EG),diethylene glycol (DEG), 1,2-propylene glycol (PG), 1,3-propyleneglycol, triethylene glycol, tetraethylene glycol, glycerol, hexyleneglycol and similar solvents. The polyol solvent may contain some water,typically in the range of less than 20 wt. %.

Optionally, protective colloids, stabilizers and/or wetting agents maybe used.

Suitable protective colloids are polysaccharides such as alginates,arabic gum, gelatine, xanthane gum, gum traganth or cellulose. Whenusing protective colloids, the metal concentration in the process can beincreased while avoiding the problem of particle agglomeration. Aftercompletion of the reaction, the protective colloid can be destroyed bytreating the suspension at temperatures in the range of 100 to 110° C.for 30 to 120 mins in an acidic (pH 0.2 to 2) or alkaline environment(pH 8 to 12).

As support materials, carbon blacks, graphitised carbon blacks,graphites, activated carbons, carbon nanoparticles, carbon nanotubes, orinorganic oxides with specific surface areas (BET surface areas measuredaccording to DIN 66132) in the range of about 30 to 2000 m²/g arepreferably used for the catalysts. Examples for suitable carbon blackmaterials are Vulcan XC 72R (Cabot Inc.) or Ketjenblack EC 300(Akzo-Nobel).

Examples for high surface area inorganic oxides are alumina, titaniumdioxide (e.g. P25, Degussa, Duesseldorf) or silica (e.g. Aerosil 200,Degussa, Duesseldorf). If the catalyst is intended for use aselectrocatalyst in fuel cells, a highly electrically conductive supportmaterial is chosen. If the catalyst is used for gas-phase reactions suchas CO-oxidation (PROX) or for purification of exhaust gases (automotivecatalysts), preferably high surface area alumina or mixed oxides, suchas alumina/silica are employed.

Typically, the concentration of the alloy components M1 and M2 on thesupport material is in the range of 1 to 90 wt. %, preferably in therange of 10 to 80 wt. % based on the total weight of the catalyst.

In the case of M1=Ru and M2=Pt, the atomic ratio of Pt to Ru (M2/M1) inthe catalyst is adjusted in a range between 4:1 to 1:4, preferably in arange of about 1:1. The concentration of platinum and ruthenium on thesupport material is in the range of 1 to 90 wt. %, preferably in therange of 10 to 80 wt. % based on the total weight of the catalyst.

The lattice constants of the supported PtRu(1:1)-catalysts manufacturedaccording to the present invention are—due to the high degree ofalloying—lower than 0.3850 rim, preferably lower than 0.3840 nm. Thesevalues apply also to the ternary PtRu(1:1)Au catalysts with a goldcontent of 0.1 to 5 wt. % based on the total weight of the catalyst.

The PtRu and PtRuAu alloy catalysts prepared according to the inventionare characterized by a very good tolerance to poisoning by carbonmonoxide (CO) and, furthermore, by an excellent performance as anodecatalysts in DMFC. Furthermore, they are very well suited for COoxidation processes (PROX) and for automotive applications. Due to thehigh degree of alloying, they do not contain any free Ru particles,which may be detrimental to the catalyst performance.

In the case of M1=base metal and M2=noble metal, the atomic ratio of thenoble metal (preferably Pt) to the base metal (M2/M1) in the catalystsis adjusted in a range between 5:1 and 1:1, preferably in a range ofabout 3:1. Again, the concentration of the noble metal(s) and the basemetal on the support material is in the range of 1 to 90 wt. %,preferably in the range of 10 to 80 wt. % based on the total weight ofthe catalyst. These ratios also apply also for ternary Pt alloyscontaining base metals, such as PtCoAu or PtCoPd, wherein the secondnoble metal (other than Pt) is present in an amount of 0.1 to 5 wt. %based on the total weight of catalyst.

The lattice constants for the Pt₃Co catalysts manufactured according tothe present invention are—due to the high degree of alloying—lower than3.870 nm.

The base metal containing noble metal alloy catalysts prepared accordingto the present invention are excellent catalysts for fuel cellapplications (e.g. cathode catalysts for PEMFC and DMFC). Generally,they show a higher activity in the cathodic oxygen reduction reaction(ORR) compared to their non-alloyed or incompletely alloyedcounterparts.

The invention is explained in more detail in the following examples andthe comparative example (CE 1) without limiting its scope of protection.

EXAMPLES Example 1 50 wt % PtRu/C Alloy Catalyst

12.0 g Ru(III)-chloride (aqueous solution with 20 wt. % Ru; Umicore,Hanau/Germany) were taken in 500 ml 1,2-propylene glycol (PG) in areaction flask. After stirring for 30 min at 300 rpm, conc. NaOHsolution was added to obtain the desired pH value of 5.5.

In the next step, 1.75 g arabic gum (Merck AG; Darmstadt/Germany,previously dissolved in 10 ml of water under mixing) were added to theabove reaction mixture by rinsing the beaker with 50 ml polyol. After 30min mixing, 7.0 g carbon black Vulcan XC 72R (Cabot Corp., Billerica,Ma./USA) was added to the mixture. After 1 hour of mixing, the contentof the flask was heated up to 150° C.

After the mixture has adjusted to this temperature, the Pt precursor wasadded. 18.4 g chloroplatinic acid (H₂PtCl₆, aqueous solution with 25 wt.% Pt; Umicore, Hanau/Germany) dissolved in 100 ml 1,2-propylene glycol(PG) were slowly added into the flask with a dropping funnel. Thetemperature of the reaction mixture was then increased to the boilingtemperature of PG (T_(bp)=188° C.). The final temperature was maintainedfor 30 min.

The slurry was then cooled to 150° C. Then 275 ml of cold DI water wasadded to bring the temperature to 100° C. At this point, conc. HClsolution was added to attain a pH value of 0.8 and the temperature wasmaintained between 100 and 110° C. for 120 mins in order to hydrolyzethe arabic gum. Stirring was continued for additional 30 mins. When thesystem cooled to room temperature, the solids were allowed to settledown and the solvent was decanted.

The solid residue was washed with 500 ml of an 1:1 ethanol-watersolution for 10 min and allowed to settle down. This step was repeatedonce and then once again washed with 500 ml DI water. Finally, the solidresidue was filtered under vacuum and was transferred to a desiccatorfor drying.

Catalyst Characterisation:.

Composition: 50 wt. % PtRu on Vulcan XC72R

Pt/Ru ratio: 1:1 (atomic ratio)

Crystallite size 2.3 nm (by XRD)

Lattice constant: 0.3824 nm (by XRD)

Degree of alloying: high

Comparative Example (CE 1)

For comparison, example 2 of U.S. Pat. No. 6,552,960 was reproduced. Invariation to the description, a high surface area carbon black support(Black Pearls 2000) was used instead of activated arbon.

1.9 g of RuCl₃×3 H₂O (35.8 wt. % Ru; Umicore, Hanau/Germany) weredissolved in 400 ml of 1,2-ethylene glycol (EG) for 30 mins. Inparallel, 3.3 g of H₂PtCl₆×H₂O (40 wt. % Pt, Umicore, Hanau/Germany)were dissolved in 400 ml of the same solvent.

2 g of carbon black (Black Pearls 2000; Cabot Corp., Billerica,Mass./USA) were suspended in 900 ml of 1,2-ethylene glycol for 30 mins.

The Ru- and the Pt-salt solution were mixed together and poured into thecarbon black suspension. After further mixing for 30 mins, thesuspension was heated to the boiling point of 1,2-ethylene glycol(T_(bp)=197° C.) and refluxed for 1 hour.

Then the suspension was filtered and the solid residue was washed withDI water and dried under vacuum overnight. As a result, a 50 wt. % PtRucatalyst was obtained.

Catalyst Characterisation:

Composition: 50 wt. % PtRu on Black Pearls 2000

Pt:Ru ratio: 1:1 (atomic ratio)

Crystallite size: 7.1 nm (by XRD)

Lattice constant: 0.3888 nm (by XRD)

Degree of alloying: low (incomplete alloying)

Example 2 50 wt. % PtCo/C Alloy Catalyst

550 ml diethylene glycol (DEG) were introduced into a three-neckedflask. 1.75 g of arabic gum (previously dissolved in 10 ml DI water for1 hour) were transferred to the polyol using an additional 50 ml of DEG.The arabic gum/DEG mixture was mixed at 500 rpm for 30 minutes.

Then, 3.5 g carbon black (Vulcan XC72R, Cabot Inc.) were dispersed inthe arabic gum/DEG solution and the dispersion was stirred for 1 morehour.

0.57 g Co(II)-hydroxide carbonate (56.1 wt. % Co; OMG, Cleveland,Ohio/USA) were added to the flask using 50 ml DEG. The mixture wasstirred for 30 mins. Then the temperature of the flask was increased to85° C.

At this temperature, 42.43 g of (EA)₂Pt(OH)₆ (aqueous solution, 7.47 wt.% Pt; Umicore, Hanau/Germany) were added to the flask, using 50 ml DEG,followed by 1 hour of stirring at 500 rpm. During stirring, the pH wasadjusted at 6.0±0.1 with acetic acid.

The flask was heated at the boiling point of DEG (T_(bp)=246° C.) andkept at that temperature for 2 hours. After the reduction was complete,the reaction mixture was cooled down at room temperature and 300 ml DIwater were added.

After settling of the catalyst particles, the top solution was siphonedoff, and 300 ml DI water were added. After the solids have settledagain, the top solution was further siphoned off; this procedure wasrepeated three times. The catalyst was then filtered and washed on thefilter repeatedly with DI water until a colorless washing liquor wasobtained.

Catalyst Characterisation:

Composition: 50 wt. % PtCo on Vulcan XC72R

Pt:Co ratio: 3:1 (atomic ratio)

Crystallite size: 2.8 nm (by XRD)

Lattice constant: 0.3867 nm (by XRD)

Degree of alloying: high

Example 3 PtRuAu/C Alloy Catalyst

550 ml 1,2-propylene glycol (PG) were introduced into a 1 l three-neckedflask. 1.25 g of arabic gum (previously dissolved in 10 ml DI water)were transferred to the polyol using additional 50 ml of PG. The arabicgum/PG mixture was mixed at 500 rpm for 30 more minutes.

Then, 2.5 g of carbon black (Ketjenblack EC-300J, AKZO Nobel,Amers-foort/The Netherlands) were dispersed in the arabic gum/PGsolution and the dispersion was stirred for 1 additional hour.

In the next step, 4.63 g Ru(III)-chloride (aqueous solution with 18.3 wt% Ru, Umicore Hanau/Germany) were added to the flask using 50 ml PG, thestirring speed was changed to 350 rpm and the pH was adjusted to 5.5with NaOH.

The flask was heated to 150° C., and then a mixture of 4.08 g CPA(Chloroplatinic acid, 39.66 wt. % Pt, Umicore, Hanau/Germany) and 0.107g of AuCl₃ (aqueous solution with 23.15 wt. % Au; Umicore,Hanau/Germany) in 100 ml PG was prepared. After the pH was pre-adjustedto 5.5 with NaOH, the mixture was added to the flask.

The flask was heated to the boiling point of PG (T_(bp)=188° C.) andkept at that temperature for 30 mins. After the reduction was complete,the reaction mixture was cooled down to 100° C. and 100 ml DI water wereadded.

At this point, conc. HCl solution was added to attain a pH value of ˜0.8and the temperature was maintained. between 100 and 110° C. for 2 hoursin order to hydrolyse the arabic gum. The system was cooled to roomtemperature and 200 ml DI water were then added.

After settling of the catalyst, the top solution was siphoned off, and300 ml DI water were added. After the solids have settled again, the topsolution was further siphoned off; this procedure was repeated threetimes. The catalyst was then filtered and washed on the filterrepeatedly with DI water until a colorless washing liquor was obtained.

Catalyst Characterisation:

Composition: 50 wt. % PtRu+0.5 wt. % Au on Ketjenblack EC 300

Pt:Ru ratio: 1:1 (atomic ratio)

Crystallite size: <2 nm (by XRD)

Lattice constant 0.3839 nm (by XRD)

Degree of alloying: high

1-18. (canceled)
 19. A supported platinum-ruthenium alloy catalyst withthe atomic ratio Pt:Ru=1:1, wherein the crystallite size is less than 3nm and the lattice constant is lower than 0.3850 nm (by XRD).
 20. Asupported platinum-ruthenium alloy catalyst according to claim 19,further comprising 0.1 to 5 wt. % gold, based on the total weight of thecatalyst.
 21. A supported platinum-ruthenium alloy catalyst according toclaim 19, wherein the concentration of platinum and ruthenium on thesupport is in the range of 1 to 90 wt. % based on the total weight ofthe catalyst.
 22. A supported platinum-ruthenium alloy catalystaccording to claim 21, wherein the concentration of platinum andruthenium on the support is in the range of 20 to 80 wt. % based on thetotal weight of the catalyst.
 23. A supported platinum-ruthenium alloycatalyst according to claim 20, wherein the concentration of platinum,ruthenium and gold on the support is in the range of 1 to 90 wt. % basedon the total weight of the catalyst.
 24. A supported platinum-rutheniumalloy catalyst according to claim 23, wherein the concentration ofplatinum, ruthenium and gold on the support is in the range of 20 to 80wt. % based on the total weight of the catalyst.
 25. A supportedplatinum-cobalt alloy catalyst with the atomic ratio Pt:Co=3:1, whereinthe crystallite size is less than 3 nm and the lattice constant is lowerthan 0.3870 nm (by XRD).
 26. A supported platinum-cobalt alloy catalystaccording to claim 25, wherein the concentration of platinum and cobalton the support is in the range of 1 to 90 wt. % based on the totalweight of the catalyst.
 27. A supported platinum-cobalt alloy catalystaccording to claim 26, wherein the concentration of platinum and cobalton the support is in the range of 20 to 80 wt. % based on the totalweight of the catalyst.
 28. An electrocatalyst for fuel cells comprisingthe catalyst according to claim
 19. 29. A gas-phase catalyst for COoxidation or exhaust gas purification comprising the catalyst accordingto claim
 19. 30. An electrocatalyst for fuel cells comprising thecatalyst according to claim
 25. 31. A gas-phase catalyst for COoxidation or exhaust gas purification comprising the catalyst accordingto claim
 25. 32. A cathode catalyst for polymer electrolyte fuel cells(PEMFC) or direct methanol fuel cells (DMFC) comprising the catalystaccording to claim 25.